[TheOtherHobbes]

Pop and jazz have "the pocket", which is where the groove clicks into maximum effectiveness.

Classical has phrasing.

IMO it's the same phenomenon. It's one of the most effective ways to add expression, and it's mostly taught aurally. There's very little in books for beginners about it.

If you're taught to play metronomically, you may never understand why it matters. Someone who is naturally musical will feel it without being told about it, but may still struggle to bring it out of their playing.